The present invention relates to a semiconductor device and a method of manufacturing a semiconductor device.
The semiconductor device described in Japanese Unexamined Patent Application Publication No. 2016-66674 (Patent Document 1) has conventionally been known. The semiconductor device described in Patent Document 1 has a MONOS (metal oxide nitride oxide silicon) transistor, a low voltage MISFET (metal insulator semiconductor field effect transistor) and a high voltage MISFET.
The MONOS transistor has an ONO (oxide nitride oxide) film to be placed on the main surface of a semiconductor substrate. The ONO film is made of a first oxide film located on the side of the semiconductor substrate, a nitride film placed on the first oxide film, and a second oxide film placed on the nitride film. The high voltage MISFET has a first gate insulating film placed on the main surface of the semiconductor substrate. The low voltage MISFET has a second gate insulating film placed on the main surface of the semiconductor substrate. The first gate insulating film is thicker than the second gate insulating film.